This NIH Ischemic SCOR has devoted itself during its first year of activity to developing new means of identifying, localizing and sizing myocardial infarct in experimental animals and in patients. In addition, considerable effort has been expended to identify the role of cell swelling, lysosomal changes, and other pathophysiological alterations occurring during myocardial ischemia that might be responsible for perpetuating the ischemic process. The latter studies have been performed with the expectation that from a better understanding of the pathophysiological processes occurring in myocardial ischemia might come certain physiological or pharmacological interventions that would effectively limit infarct size in experimental animals and in man. The major accomplishments of our Ischemic SCOR activity over the past 11 months include the following: 1) the further development and utilization of technetium-99m stannous pyrophosphate (Tc99m-PYP) myocardial scintigrams to identify the presence of, localize and size acute myocardial infarcts in experimental animals and in man, 2) the development of "combined myocardial imaging" using both thallium-201 and Tc99m-PYP in order to identify and size old and new areas of myocardial damage in experimental animals and in man, 3) a clear understanding of the pathophysiology involved in the development of abnormal Tc99m-PYP and thallium-201 myocardial scintigrams during myocardial infarction, 4) a better understanding of the role of cell swelling and its temporal relationship to the duration of myocardial ischemia, altered sodium, potassium ATPase myocardial tissue activity and its role in altering coronary blood flow, 5) the development of methods to measure localized ventricular wall motion and thickness during myocardial ischmia which should serve as a very sensitive indicator of localized ventricular function, 6) an investigation of alterations in cardiac lysosomes that occur during hypoxia and ischemia, 7) the development of "isopotential ECG surface maps" in order to be able to localize the site of injury with various types of infarcts in patients and hopefully, ultimately to be able to electrocardiographically size the area of damage, and 8) studies directed at defining the timing, location and severity of alterations in membrane integrity in myocardial cells and subcellular structures during myocardial i (Text Truncated - Exceeds Capacity)